Unified dual loop linear active disturbance rejection control for grid connected axial field flux switching permanent magnet wind turbines

The large-scale integration of direct-drive wind turbines into weak grids imposes stringent requirements on grid-side converters, including robust DC-link voltage regulation, high power quality, and fault ride-through capability. Conventional PI control and partial LADRC implementations suffer from limited disturbance rejection and lack a unified control architecture. This paper presents a Unified Dual-Loop Linear Active Disturbance Rejection Control (UDL-LADRC) framework for the grid-side converter of a direct-drive wind turbine employing a novel Axial Field Flux-Switching Sandwiched Permanent Magnet Machine with Twisted Structure (AFFSSPM-TS). The framework uses a second-order LADRC for the DC-link voltage outer loop and first-order LADRCs for the dq current inner loops, ensuring consistent disturbance estimation and rejection across all control layers. A Least Error Squares (LES) filter is integrated for rapid and accurate grid voltage detection during faults, enabling precise reactive current injection for low-voltage ride-through. Experimental validation was conducted on a 700 W hardware platform using a dSPACE DS1103 real-time system under wind speed variations, voltage sags and swells, weak grid conditions, and harmonic-distorted grids. The proposed UDL-LADRC reduced the DC-link voltage deviation to within ± 1.1% during wind speed variations (compared to ± 11.3% for PI control), with a recovery time of 0.09 s (compared to 0.25 s for PI). During voltage swells, the voltage deviation was limited to 4.2% with a recovery time of 24 ms. The active power settling time was 0.05 s, and the grid current THD remained below 3.1%. Under weak grid conditions, the current tracking error was below 3.5% RMS. The controller also provided stable reactive power support during a 66% voltage sag. The unified architecture provides synergistic benefits over partial implementations, including hierarchical disturbance rejection, prevention of cross-loop disturbance propagation, and consistent model-independent tuning. The proposed UDL-LADRC is a robust, grid-code-compliant, and computationally feasible solution for AFFSSPM-TS-based wind energy conversion systems.